The cytochrome bo ubiquinol oxidase from Escherichia coli is a five-subunit enzyme which is a member of the superfamily of heme-copper respiratory oxidases. Three of the subunits (I, II, and III) are homologous to the three mitochondrial encoded subunits of the eukaryotic aa3-type cytochrome c oxidase. Subunits, I, II, and III of the eukaryotic oxidase contain 12, 2, and 7 putative transmembrane spans, respectively. The hydropathy profiles of the subunits of most other members of this oxidase superfamily are consistent with these structures. However, subunit I from the E. coli oxidase contains 15 transmembrane spans, with one additional span at the N-terminus and two additional spans at the C-terminus in comparison to the eukaryotic oxidase. The additional transmembrane helix at the N-terminus predicts that the amino terminal residue should be on the periplasmic side of the membrane. By deleting the intergenic region between the cyoA and cyoB genes, an in-frame fusion between subunit II (cyoA) and subunit I (cyoB) was generated. This links the C-terminus of subunit II, known to be on the periplasmic side of the membrane, to the N-terminus of subunit I. The resulting oxidase is fully active, and supports the toplogical folding pattern previously suggested for subunit I with the N-terminus in the periplasm. Whereas subunit I of the E. coli oxidase has two additional membrane-spanning helices at the C-terminus, subunit III has two fewer helices than does the corresponding subunit III of the eukaryotic oxidase.(ABSTRACT TRUNCATED AT 250 WORDS)

译文

来自大肠杆菌的细胞色素bo泛醇氧化酶是一种五亚基酶,是血红素铜呼吸氧化酶超家族的成员。三个亚基 (I,II和III) 与真核aa3-type细胞色素c氧化酶的三个线粒体编码亚基同源。真核氧化酶的亚基I,II和III分别包含12、2和7个推定的跨膜跨度。该氧化酶超家族大多数其他成员的亚基的亲水谱与这些结构一致。然而,与真核氧化酶相比,来自大肠杆菌氧化酶的亚基I包含15个跨膜跨度,在N末端增加一个跨度,在C末端增加两个跨度。N末端的附加跨膜螺旋预测氨基末端残基应在膜的周质侧。通过删除cyoA和cyoB基因之间的基因间区域,生成了亚基II (cyoA) 和亚基I (cyoB) 之间的框架内融合。这将亚基II的C端 (已知位于膜的周质侧) 连接到亚基I的N端。所得的氧化酶具有完全活性,并支持先前建议的亚基I在周质中具有N末端的顶折叠模式。大肠杆菌氧化酶的亚基I在C末端有两个额外的跨膜螺旋,而亚基III比真核氧化酶的相应亚基III少两个螺旋。(摘要截短于250字)

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